Mouthpiece valves for breathing equipment typically employ two pins directly connected to the valve disc. The valve disc is moved along the axis of the valve stem by the user's lips in order to open the valve. The two pins are in turn displaced by the movement of the valve disc. Such a mouthpiece valve is shown in U.S. Pat. No. 4,090,511. The disadvantage with this device is that there is no means of preventing premature movement of the pins and disc and thus the opening of the valve since the pins can be axially displaced at any time prior to the intended opening of the valve. The resultant unintended opening of the valve is particularly undesirable for two reasons. First, it is possible to expend an indeterminate portion of the air stored in the breathing equipment. Also, the user may be unaware of this escape because the valve disc may subsequently be returned to the closed position, thereby concealing the escape. The user would then have only a fraction of the anticipated capacity of the breathing equipment available for use. Secondly, if the mouthpiece valve is used in breathing equipment which is deployed underwater, when the valve disc moves water can flow through the valve into the breathing equipment. If the breathing equipment uses a chemical canister, this could render it unusable.
It would be desirable therefore to provide a mechanism for reliably locking the mouthpiece valve in the closed position during storage and transport so that the user can be assured that the first time valve is opened is when the user intentionally opens it during use. Furthermore, the locking means should be able to be quickly and easily unlocked, preferably in a single motion by the user, at the desired time when the breathing equipment is to be used.